The present invention relates to temperature responsive devices and in particular to containers having meltable bodies therein.
Meltable devices are generally used for fire sprinkling systems, slow-blow fuses, thermal overload devices for electrical motors etc. Known thermal switches employ a metallic conductor that has a preselected melting point. This metallic conductor is arranged so that when this preselected temperature is exceeded, the element parts, interrupting the electrical current flowing through it. These known devices employ relatively expensive, toxic metal alloys, such as bismuth, antimony, tin, lead, cadmium, or mercury. In addition, being metallic these devices have electrical limitations. Care must be taken that melted elements do not inadvertently short adjacent circuitry. Furthermore, these metallic alloys have relatively higher melting points which limit their applications.
It is desirable to have a thermally responsive device which can actuate electrical, fluidic or mechanical devices. In addition it is desirable to have a simple thermal device which provides a visual indication of whether a predetermined temperature has been exceeded. It is also desirable that the thermal device be designable to operate reversibly or irreversibly.
The present invention can provide these features and advantages by employing an actuating member and a meltable body within a container. In one embodiment a spring loaded switch is held in a closed position by a surrounding medium such as paraffin. This thermal switch can be designed to open at a relatively moderate temperature. Moreover, if a non-conductor such as paraffin is employed electrical operation is not significantly affected by this meltable medium. Accordingly, contact design can be implemented without undue concern for the strength or conductivity associated with the meltable medium. In addition, such a spring loaded switch can be designed so that if temperature recedes and the meltable medium solidifies, the switch does not reset. Alternativley, the electrical contacts for the spring loaded switch can be physically located outside the meltable medium. this feature allows the electrical contacts to operate without touching the meltable medium.
In another embodiment of the present invention a multiplicity of conductive granules are embeded in a meltable body at the interspace between two electrodes. This device is arranged so that when the meltable body melts the metallic granules migrate with respect to these electrodes. This arrangement can be designed to provide either a normally closed or open switch. The migration characteristics of the granules can be influenced by an electromagnet which can cause the granules to migrate in any direction including upward.
In another embodiment a meltable plug is used to hold a valve member against a valve seat. Upon melting of the meltable body the valve is opened by fluid pressure.
In a situation where physical operation of accessories is not desired, a device incorporating principles of the present invention employs a transparent container so that temperature conditions are indicated visually. For example, a weight in the upper part of a transparent container may be supported by a meltable body. In the event a predetermined temperature is exceeded, the weight decends through the melted medium thereby providing a visual indication of excessive temperatures. Such an arrangement can be reversible. Thus, the transparent container can be inverted and heated to restore the weight to its original position.